The deepest and longest train tunnel in the world just opened — claustrophobics beware

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One of the great engineering marvels of the 21st century has finally reached completion.

The Gotthard Base Tunnel, the longest and deepest train tunnel in the world, opened on June 1. It offers unprecedented efficiency for passengers and cargo moving between northern and southern Europe — instead of driving trucks around the Alps, travelers can now sail straight through them on high-speed trains.

The entire project lasted 17 years and cost more than $23 billion. In the end, nine workers died making the tunnel a reality.

The project actually involves two separate, parallel tunnels. The northern ends are in Rotterdam, the Netherlands and the southern ends are in Genoa, Italy.

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Each tunnel is 35 miles long. At their deepest points, they burrow nearly a mile and a half below the surface. At that level, the rock can reach temperatures upward of 115 degrees.

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Boring through the mountains' layers was no easy feat. Engineers had to clear away 73 different types of rock, which ranged from the consistency of sugar to the hardness of solid granite.

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Thanks to five different access points along the tunnels' path, builders were able to cut their construction time in half by working at different sites simultaneously. The two tunnels are connected roughly every 1,000 feet.

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Workers had many different duties while assembling the tunnel, such as gauging precise measurements ...

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... regulating how much concrete to pour for each piece of track ...

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... and overseeing construction from the staff train, called Helvetia, which traveled the length of the tunnel during construction to carry supplies and assist with labor.

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The tubes measure approximately 30 feet in diameter and span more than 90 total miles including ancillary shafts and service tunnels.

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That may or may not console those with claustrophobic leanings.

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Trains will run approximately 155 mph on the tracks, allowing for transport between Zurich, Switzerland and Milan, Italy in less than three hours.

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For now, the tunnel will be operating with limited service. Full service is expected to begin in December.

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The European Union is already hailing the Gotthard Base Tunnel as a unifying achievement for the region. Countries that used to be separated by natural borders ...

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... are now more connected thanks to the wonders of modern engineering.